Introduction
In the realm of sports and athletics, one concept has a huge impact on performance, yet remains largely misunderstood – the Stretch-Shortening Cycle (SSC). SSC is a muscle action that capitalizes on the ‘elastic’ properties of muscles and tendons to generate increased force.
Imagine a spring: it’s first stretched out, and when released, it springs back forcefully. Similarly, our muscles and tendons, when stretched (eccentric contraction) before shortening (concentric contraction), produce greater force and power.
The application of SSC is not confined to any specific sport – it is a universal principle that underpins a vast array of athletic movements, and training to improve the efficiency of one’s own SSC can lead to a large increase in performance.
Whether you’re a sprinter exploding off the blocks, a basketball player leaping for a dunk, or a tennis player delivering a powerful serve, the SSC is at play.
In this blog post, I’ll explore the intricacies of the SSC, its role in sprinting and explosivity, and how athletes can effectively integrate it into their training regimes.
Understanding the Biomechanics of SSC
The Eccentric Phase (Lengthening or Stretch)
The stretch-shortening cycle commences with the eccentric phase. This is when the muscle lengthens under tension, much like a stretched rubber band.
It’s the preparatory stage for movement – think of the runner’s muscles coiling in anticipation of the gun, or the downward phase of a jump. The eccentric phase stores potential energy in the muscle-tendon unit, which can be utilized in the following phases.
The Amortization Phase (Transition)
Following the eccentric phase is the amortization or transition phase. It’s a brief period where the muscle is neither lengthening nor shortening – the ‘pause’ between the stretch and the contraction.
The importance of this phase lies in its brevity. Too long a pause can lead to a dissipation of the stored elastic energy.
The aim is to transition from the eccentric to the concentric phase as swiftly as possible to optimize power output. In the context of sprinting, this can be thought of as your ground contact time (shorter times = faster transition).
The Concentric Phase (Shortening)
The final phase is the concentric phase. The stored energy from the eccentric phase is released as the muscle contracts and shortens.
This is the phase where the actual movement occurs – the sprinter bursting forward, the athlete leaping into the air. The SSC enhances the force produced during this phase, leading to increased performance.
A diagram showing the stages of SSC during a vertical jump
How these phases contribute to SSC
In an effective SSC, these three phases occur in rapid succession, each building upon the other to maximize force production.
The SSC uses the inherent elasticity of our muscles and tendons, akin to a biological spring mechanism, to enhance performance across a wide array of athletic movements.
A simple way to understand the SSC is to think about doing a squat jump (starting in a squat position and jumping as high as you can) versus doing a counter-movement jump (where you quickly lower yourself into a squat position before jumping).
The second movement incorporates the SSC, whereas the first does not. Therefore, unsurprisingly, peoples’ counter-movement jump is generally higher than their squat jump.
The Role of SSC in Sprinting
The science behind SSC and sprinting
Sprinting is a classic example of SSC in action, where the cyclical movement of the legs utilizes all three phases of the SSC.
When the foot makes contact with the ground, the muscles and tendons in the leg lengthen under tension (the eccentric phase).
The brief moment when the foot is planted firmly on the ground is the amortization phase.
Finally, the shortening of muscles as the foot pushes off the ground for the next stride is the concentric phase. This cycle repeats with each stride, allowing for the powerful and rapid movements required in sprinting.
This diagram does a good job at showing the three phases of the SSC during a step. This is why, generally speaking, the more efficient you SSC is, the shorter ground contacts you have when sprinting.
Importance of SSC in achieving top speed
SSC is crucial in achieving top sprinting speed. The quick transition from eccentric to concentric contraction during each stride allows for a greater force to be applied to the ground, resulting in increased stride frequency.
The role of SSC in maintaining speed
Once top speed is reached, the SSC continues to play a vital role. The rapid and repeated SSCs in each stride help to maintain speed with optimal energy efficiency. Understanding and improving the efficiency of one’s SSC can therefore lead to significant improvements in sprint performance.
This slow-motion video of Usain Bolt sprinting allows us to really see the SSC in action at during ground contact. Faster sprinters have lower ground contact times ~ more efficient SSC.
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SSC and Explosivity: Enhancing Power and Speed
How SSC improves jump performance
The vertical jump, commonly used in sports like basketball and volleyball, is a powerful demonstration of SSC.
As the athlete bends their knees and hips in preparation (the eccentric phase), potential energy is stored.
A swift transition (the amortization phase) then leads to a rapid straightening of these joints (the concentric phase), propelling the athlete upwards. The stored energy from the SSC contributes to a higher, more powerful jump.
As mentioned the SSC is present across a range of athletic movements, and not just sprinting. Above you can see how fast the cycles are for various athletic movements.
The impact of SSC on throwing and striking
In activities such as throwing a baseball, hitting a tennis ball, or striking a boxing punch, the SSC is critical.
The initial backward movement (eccentric phase) stretches the relevant muscles and tendons, storing potential energy.
A quick transition (amortization phase) then leads to a powerful forward motion (concentric phase), releasing the stored energy and propelling the ball, racket, or fist forward with enhanced speed and force.
Enhancing agility and quickness with SSC
In sports where quick directional changes are essential, such as soccer or American football, SSC is vital.
The rapid sequence of eccentric and concentric contractions during quick movements, stops, and changes of direction can significantly enhance an athlete’s agility and quickness. By understanding and leveraging the SSC, athletes can improve their on-field performance in these critical aspects.
As you can see from the previous couple of sections, athleticism is seldom isolated to a single area – usually those are fast can also jump higher and change direction more seamlessly (and vice-versa).
Applying SSC in Athletic Training
Specific exercises to optimize SSC (plyometrics, resistance training, etc.)
Various training methods can help optimize SSC. Plyometric exercises, like jump squats, broad jumps, and depth jumps, can enhance the eccentric and concentric phases of the SSC. On this website I have a full library of plyometric exercises if you’re interested in learning more about the various types of plyometric exercises that exist.
Resistance training, particularly eccentric loading, can also help improve the strength and elasticity of muscles and tendons, contributing to a more efficient SSC.
Pogo jumps are one of my favourite exercises to target elasticity in the lower limbs for sprinters. You can find out more about Pogo Jumps here.
Training programs focusing on SSC enhancement
When creating a training program, it’s important to incorporate exercises that target all three phases of SSC. Such a program may include a mix of plyometrics, resistance training, and sport-specific drills.
It’s also important to progressively increase the intensity and complexity of these exercises to continuously challenge and enhance the SSC.
Misconceptions about SSC
Like any scientific concept, SSC is not immune to misconceptions and misunderstandings. One common myth is that SSC is only relevant for elite athletes. The truth is, whether you’re an amateur or a professional, understanding and utilizing SSC can enhance your performance.
Even though ‘the SSC’ sounds fancy and ‘advanced‘, SSC is a natural biomechanical process that occurs in our bodies during many movements. Training to optimize this process simply involves enhancing the natural abilities of our muscles and tendons.
Conclusion
In the world of athletics, success often hinges on minute details, and the Stretch-Shortening Cycle (SSC) is one such detail that holds the potential to drastically enhance performance. By understanding the mechanics of SSC – from the initial eccentric phase of muscle lengthening to the final burst of power in the concentric phase – athletes can tap into their body’s natural ‘spring’ mechanism to maximize speed, power, and explosivity.
Whether it’s in the context of sprinting, jumping, throwing, or changing direction quickly, the principles of SSC are universal and can be applied across all sports. Through targeted training and injury prevention strategies, athletes can improve their SSC efficiency, leading to significant performance gains.
